LeetCode 367. Valid Perfect Square

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Follow up: Do not use any built-in library function such as sqrt.

 

Example 1:

Input: num = 16
Output: true

Example 2:

Input: num = 14
Output: false

 

Constraints:

• 1 <= num <= 2^31 - 1

 

Solution:

class Solution {
    public boolean isPerfectSquare(int num) {
        long left = 0;
        long middle = 0;
        long right = num;
        while (left <= right){
            middle = (left + right) / 2;
            long squared = middle * middle;
            if (squared == num){
                return true;
            } else if (squared > num){
                right = middle - 1;
            } else {
                left = middle + 1;
            }
        }
        return false;
    }
}